1. Field of the Invention
The present invention relates to a method for detecting the semiconductor melt temperature by means of video signals of a video camera in the Manufacturing process of a single-crystal semiconductor according to the Czochralski method.
2. Description of Related Art
The Czochralski (hereafter CZ) method, according to which a single-crystal rod is pulled from the melt inside a crucible, is one of the conventional methods for producing single-crystal silicon which is used as fundamental material of a semiconductor integrated circuit. In the CZ method, polycrystal silicon of high purity is charged into a crucible inside a main chamber of a single-crystal manufacturing apparatus. The polycrystal silicon is then melted by heaters arranged around the crucible. When a seed held by a seed holder is immersed in the melted polycrystal silicon, and is pulled while rotating the seed holder and the crucible in the same or opposite direction each other , and then a single-crystal rod is grown.
FIG. 6 is a schematic diagram illustrating the structure of a conventional single-crystal semiconductor manufacturing apparatus using the CZ method. The apparatus includes a metal wire rolling motor 31, a metal wire rolling drum 32, and another motor 33 for driving a vacuum container in which the metal wire rolling motor 31 and the metal wire rolling drum 32 are installed. When the wire cable 34 is rolled, a single-crystal produced from a seed can be driven to rotate. The apparatus further includes a TV camera 35, a transparent quartz window 36 and a seed holder 37 for fixing the seed. In the figure also illustrates the melt surface 38, a graphite heater 39 for melting the polysilicon material in the crucible, a graphite heat insulator 40, a motor 41 for rotating the crucible by driving the crucible pedestal and a crucible elevator 42.
When the single-crystal silicon is pulled, the TV camera 35 traces a meniscus ring between the melt surface 38 and the single-crystal silicon, and generates image signals to a radiation thermometer unit 44 through a camera controller 43, thereby calculating the diameter of the single-crystal silicon across the meniscus ring. Moreover, the diameter of the single-crystal silicon is controlled to meet a predetermined value by means of a diameter controller 45 which is provided for controlling the pulling rate of the seed and the melt temperature. Furthermore, a TV monitor 46 is provided.
In the aforementioned single-crystal silicon manufacturing apparatus, before normal growth of single-crystal silicon, the diameter is controlled to about 3-4 mm and the length is controlled to 100-150 mm for preventing the formation of dislocation. This step for preventing dislocation forms silicon rods having a diameter of 3-4 mm, and is therefore called a necking step.
The necking step, if the temperature is not properly controlled at the beginning, will generate an abruptly slim region where the single-crystal silicon tends to separate from the melt. On the other hand, if the diameter of the single-crystal silicon is larger than 3-4 mm, the dislocation cannot be avoided. That is, when the melt temperature in the crucible rises beyond control, the single-crystal silicon in the necking step will be too narrow to maintain contact with the melt. On the contrary, if the melt temperature is too low, the diameter of the single-crystal silicon will increase to produce the dislocation.
Several methods for precisely detecting the melt temperature in the necking step have been disclosed. For example, Japanese Laid Open 4-325488 disclosed a method to control the surface temperature of the melt before immersing the seed therein, thereby improving the effect of the necking step. In order to precisely detect the surface temperature of the melt, a radiation thermometer must be vertically arranged over the melt surface, as is disclosed. Moreover, a two-color thermometer is required in the patent to detect the melt surface temperature by the radiation energy ratio of two different wavelength.
However, the melt surface in the necking step is situated in the center of the quartz crucible for containing the melt. When the two-color thermometer lies perpendicular to the melt surface, the detected region must be located more than 10 cm away from the center in order to avoid the interference of the seed holder 37, rolling drum 32 and rolling motor 33 (referring to FIG. 6).
As those skilled in the art recognized, that the temperature of the melt surface varies greatly in the vertical direction as a result of the rotation rate of the crucible, the corresponding positions of the heaters and the flow rate of argon gas conducted in the furnace. Therefore, even though the temperature of the melt surface in the detected region at a distance from the furnace center can be precisely controlled, the real temperature in the furnace center where the necking step is carried out has a vast undetermined deviation from the controlled temperature. That is, it is very difficult to control. the optimal temperature in the furnace center for the necking step.
Moreover, the cost of the two-color thermometer, as compared with general radiation thermometer for mono-wavelengths, is much higher. Furthermore, to install the two-color thermometer perpendicular to the melt surface so that it can be observed also increases the complexity of the single-crystal silicon manufacturing apparatus.